1. Technical Field:
The present invention relates in general to the field of data processing systems and in particular to methods and systems for maintaining continued availability to accessing data processing systems during backup copying of designated datasets stored within one or more storage subsystems. Still more particularly, the present invention relates to methods and systems for dynamic allocation of a buffer storage space within a data processing system during backup copying of designated datasets and indexing each designated dataset once it has been copied.
2. Description of the Related Art:
A modern data processing system must be prepared to recover, not only from corruptions of stored data which occur as a result of noise bursts, software bugs, media defects, and write path errors, but also from global events, such as data processing system power failure. The most common technique of ensuring the continued availability of data within a data processing system is to create one or more copies of selected datasets within a data processing system and store those copies in a nonvolatile environment. This so-called "backup" process occurs within state-of-the-art external storage systems in modern data processing systems.
Backup policies are implemented as a matter of scheduling. Backup policies have a space and time dimension which is exemplified by a range of datasets and by the frequency of backup occurrence. A FULL backup requires the backup of an entire range of a dataset, whether individual portions of that dataset have been updated or not. An INCREMENTAL backup copies only that portion of the dataset which has been updated since a previous backup, either full or incremental. The backup copy thus created represents a consistent view of the data within the dataset as of the time the copy was created.
Of course, those skilled in the art will appreciate that as a result of the process described above, the higher the backup frequency, the more accurately the backup copy will mirror the current state of data within a dataset. In view of the large volumes of data maintained within a typical state-of-the-art data processing system backing up that data is not a trivial operation. Thus, the opportunity cost of backing up data within a dataset may be quite high on a large multiprocessing, multiprogramming facility, relative to other types of processing.
Applications executed within a data processing system are typically executed in either a batch (streamed) or interactive (transactional) mode. In a batch mode, usually one application at a time executes without interruption. Interactive mode is characterized by interrupt driven multiplicity of applications or transactions.
When a data processing system is in the process of backing up data in either a streamed or batch mode system, each process, task or application within the data processing system is affected. That is, the processes supporting streamed or batch mode operations are suspended for the duration of the copying. Those skilled in the art will recognize that this event is typically referred to as a "backup window." In contrast to batch mode operations, log based or transaction management applications are processed in the interactive mode. Such transaction management applications eliminate the "backup window" by concurrently updating an on-line dataset and logging the change. However, this type of backup copying results in a consistency which results in a consistency described as "fuzzy." That is, the backup copy is not a precise "snapshot" of the state of a dataset/data base at a single point in time. Rather, a log comprises an event file requiring further processing against the database.
A co-pending U. S. Pat. application Ser. No. 07/385,647, filed Jul. 25, 1989, entitled A Computer Based Method For Dataset Copying Using an Incremental Backup Policy, illustrates backup in a batch mode system utilizing a modified incremental policy. A modified incremental policy copies only new data or data updates since the last backup. It should be noted that execution of applications within the data processing system are suspended during copying in this system.
As described above, to establish a prior point of consistency in a log based system, it is necessary to "repeat history" by replaying the log from the last check point over the datasets or database of interest. The distinction between batch mode and log based backup is that the backup copy is consistent and speaks as of the time of its last recordation, whereas the log and database mode require further processing in the event of a fault, in order to exhibit a point in time consistency.
U. S. Pat. No. 4,507,751, Gawlick et al., entitled Method and Apparatus for Logging Journal Data Using a Write Ahead Dataset, issued Mar. 25, 1985, exemplifies a transaction management system wherein all transactions are recorded on a log on a write-ahead dataset basis. As described within this patent, a unit of work is first recorded on the backup medium (log) and then written to its external storage address.
Co-pending U. S. Pat. application Ser. No. 07/524,206, filed May 16, 1990, entitled Method and Apparatus for Executing Critical Disk Access Commands, teaches the performance of media maintenance on selected portions of a tracked cyclic operable magnetic media concurrent with active access to other portions of the storage media. The method described therein requires the phased movement of customer data between a target track to an alternate track, diversion of all concurrent access requests to the alternate track or tracks and the completion of maintenance and copy back from the alternate to the target track.
During backup copying, the backup program acquires a buffer storage space large enough to generally hold some portion, such as a record, block track or cylinder, of a dataset. The data is read in these increments by the backup program and then written to the alternate storage system before more data is read. The backup program's performance is "paced" based on the buffer sizes used. In known data processing systems, the size of the buffer storage space acquired has been determined based on the requirements of the backup program and not on optimizing the backup copying process for the entire system including the hardware and input/output channels.
Therefore, it should be obvious that a need exists for a method and system whereby the size of a buffer storage space is determined based on considerations for the optimization of the backup copying process for the entire system including the hardware and input/output channels.